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Pharmacological targeting of the PI3K/mTOR pathway alters the release of angioregulatory mediators both from primary human acute myeloid leukemia cells and their neighboring stromal cells.

Reikvam H, Nepstad I, Bruserud Ø, Hatfield KJ - Oncotarget (2013)

Bottom Line: Hierarchical clustering analysis showed that disruption of PI3K/Akt/mTOR pathways decreased AML cell release of CXCL8-11 for a large subset of patients, whereas the effects on other mediators were divergent.Various stromal cells (endothelial cells, fibroblasts, cells with osteoblastic phenotype) also showed constitutive release of angioregulatory mediators, and inhibitors of both the PI3K and mTOR pathway had anti-proliferative effects on stromal cells and resulted in decreased release of these angioregulatory mediators.PI3K and mTOR inhibitors can decrease constitutive cytokine release both by AML and stromal cells, suggesting potential direct and indirect antileukemic effects.

View Article: PubMed Central - PubMed

Affiliation: Section for Hematology, Department of Clinical Science, University of Bergen, Norway.

ABSTRACT
Acute myeloid leukemia (AML) is a heterogeneous and aggressive malignancy with poor overall survival. Constitutive as well as cytokine-initiated activation of PI3K/Akt/mTOR signaling is a common feature of AML patients, and inhibition of this pathway is considered as a possible therapeutic strategy in AML. Human AML cells and different stromal cell populations were cultured under highly standardized in vitro conditions. We investigated the effects of mTOR inhibitors (rapamycin and temsirolimus) and PI3K inhibitors (GDC-0941 and 3-methyladenin (3-MA)) on cell proliferation and the constitutive release of angioregulatory mediators by AML and stromal cells. Primary human AML cells were heterogeneous, though most patients showed high CXCL8 levels and detectable release of CXCL10, Ang-1, HGF and MMP-9. Hierarchical clustering analysis showed that disruption of PI3K/Akt/mTOR pathways decreased AML cell release of CXCL8-11 for a large subset of patients, whereas the effects on other mediators were divergent. Various stromal cells (endothelial cells, fibroblasts, cells with osteoblastic phenotype) also showed constitutive release of angioregulatory mediators, and inhibitors of both the PI3K and mTOR pathway had anti-proliferative effects on stromal cells and resulted in decreased release of these angioregulatory mediators. PI3K and mTOR inhibitors can decrease constitutive cytokine release both by AML and stromal cells, suggesting potential direct and indirect antileukemic effects.

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Effects of mTOR and PI3K inhibitors on constitutive release of angiogenic mediators by stromal cellsThe effects of mTOR (rapamycin, temsirolimus) and PI3K inhibition (GDC-0941, 3-MA) on in vitro constitutive mediator release was investigated for 10 different stromal cell populations. Cell supernatants were harvested from stromal cell cultures before confluence was reached. Levels of each mediator were determined using ELISA, and relative values (levels in drug-treated cultures divided by levels in corresponding control cultures) were log(2) converted. Squares are omitted where no detectable levels of mediators were measured in control/treated cultures. The various stromal cell populations examined are indicated in the right column.
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Figure 5: Effects of mTOR and PI3K inhibitors on constitutive release of angiogenic mediators by stromal cellsThe effects of mTOR (rapamycin, temsirolimus) and PI3K inhibition (GDC-0941, 3-MA) on in vitro constitutive mediator release was investigated for 10 different stromal cell populations. Cell supernatants were harvested from stromal cell cultures before confluence was reached. Levels of each mediator were determined using ELISA, and relative values (levels in drug-treated cultures divided by levels in corresponding control cultures) were log(2) converted. Squares are omitted where no detectable levels of mediators were measured in control/treated cultures. The various stromal cell populations examined are indicated in the right column.

Mentions: The final effect of these drugs on angioregulation depends on their effects on the local balance between pro- and antiangiogenic mediators. Our overall results suggest that these drugs often have a relatively weak effect on proangiogenic CXCL8 that is released at high levels by AML cells for most patients; a strong inhibitory effect on this proangiogenic mediator was only seen for a subset of patients and an increased release was often seen for the stromal cells. The drugs had divergent effects on several other mediators (see Table 5 and Fig. 5) and it is possible that other growth factors/cytokines involved in AML-stroma interactions may be targeted by PI3K/mTOR inhibitors. It is therefore difficult to predict the final overall effect of these drugs on bone marrow angioregulation, though in our opinion it seems most likely that the final effect will differ between individual patients, and for many patients antiangiogenic effects do not seem to be a major contributor to the antileukemic effects seen by the investigated PI3K/Akt/mTOR inhibitors and may also involve microenvironment-mediated drug-resistance [53, 54].


Pharmacological targeting of the PI3K/mTOR pathway alters the release of angioregulatory mediators both from primary human acute myeloid leukemia cells and their neighboring stromal cells.

Reikvam H, Nepstad I, Bruserud Ø, Hatfield KJ - Oncotarget (2013)

Effects of mTOR and PI3K inhibitors on constitutive release of angiogenic mediators by stromal cellsThe effects of mTOR (rapamycin, temsirolimus) and PI3K inhibition (GDC-0941, 3-MA) on in vitro constitutive mediator release was investigated for 10 different stromal cell populations. Cell supernatants were harvested from stromal cell cultures before confluence was reached. Levels of each mediator were determined using ELISA, and relative values (levels in drug-treated cultures divided by levels in corresponding control cultures) were log(2) converted. Squares are omitted where no detectable levels of mediators were measured in control/treated cultures. The various stromal cell populations examined are indicated in the right column.
© Copyright Policy - open-access
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3757241&req=5

Figure 5: Effects of mTOR and PI3K inhibitors on constitutive release of angiogenic mediators by stromal cellsThe effects of mTOR (rapamycin, temsirolimus) and PI3K inhibition (GDC-0941, 3-MA) on in vitro constitutive mediator release was investigated for 10 different stromal cell populations. Cell supernatants were harvested from stromal cell cultures before confluence was reached. Levels of each mediator were determined using ELISA, and relative values (levels in drug-treated cultures divided by levels in corresponding control cultures) were log(2) converted. Squares are omitted where no detectable levels of mediators were measured in control/treated cultures. The various stromal cell populations examined are indicated in the right column.
Mentions: The final effect of these drugs on angioregulation depends on their effects on the local balance between pro- and antiangiogenic mediators. Our overall results suggest that these drugs often have a relatively weak effect on proangiogenic CXCL8 that is released at high levels by AML cells for most patients; a strong inhibitory effect on this proangiogenic mediator was only seen for a subset of patients and an increased release was often seen for the stromal cells. The drugs had divergent effects on several other mediators (see Table 5 and Fig. 5) and it is possible that other growth factors/cytokines involved in AML-stroma interactions may be targeted by PI3K/mTOR inhibitors. It is therefore difficult to predict the final overall effect of these drugs on bone marrow angioregulation, though in our opinion it seems most likely that the final effect will differ between individual patients, and for many patients antiangiogenic effects do not seem to be a major contributor to the antileukemic effects seen by the investigated PI3K/Akt/mTOR inhibitors and may also involve microenvironment-mediated drug-resistance [53, 54].

Bottom Line: Hierarchical clustering analysis showed that disruption of PI3K/Akt/mTOR pathways decreased AML cell release of CXCL8-11 for a large subset of patients, whereas the effects on other mediators were divergent.Various stromal cells (endothelial cells, fibroblasts, cells with osteoblastic phenotype) also showed constitutive release of angioregulatory mediators, and inhibitors of both the PI3K and mTOR pathway had anti-proliferative effects on stromal cells and resulted in decreased release of these angioregulatory mediators.PI3K and mTOR inhibitors can decrease constitutive cytokine release both by AML and stromal cells, suggesting potential direct and indirect antileukemic effects.

View Article: PubMed Central - PubMed

Affiliation: Section for Hematology, Department of Clinical Science, University of Bergen, Norway.

ABSTRACT
Acute myeloid leukemia (AML) is a heterogeneous and aggressive malignancy with poor overall survival. Constitutive as well as cytokine-initiated activation of PI3K/Akt/mTOR signaling is a common feature of AML patients, and inhibition of this pathway is considered as a possible therapeutic strategy in AML. Human AML cells and different stromal cell populations were cultured under highly standardized in vitro conditions. We investigated the effects of mTOR inhibitors (rapamycin and temsirolimus) and PI3K inhibitors (GDC-0941 and 3-methyladenin (3-MA)) on cell proliferation and the constitutive release of angioregulatory mediators by AML and stromal cells. Primary human AML cells were heterogeneous, though most patients showed high CXCL8 levels and detectable release of CXCL10, Ang-1, HGF and MMP-9. Hierarchical clustering analysis showed that disruption of PI3K/Akt/mTOR pathways decreased AML cell release of CXCL8-11 for a large subset of patients, whereas the effects on other mediators were divergent. Various stromal cells (endothelial cells, fibroblasts, cells with osteoblastic phenotype) also showed constitutive release of angioregulatory mediators, and inhibitors of both the PI3K and mTOR pathway had anti-proliferative effects on stromal cells and resulted in decreased release of these angioregulatory mediators. PI3K and mTOR inhibitors can decrease constitutive cytokine release both by AML and stromal cells, suggesting potential direct and indirect antileukemic effects.

Show MeSH
Related in: MedlinePlus